For telephone communications and the like, it is a common practice to utilize controlled environment underground vaults for housing switching gear and other electronic apparatus, terminal junctions, etc. These vaults frequently may be located under sidewalks or the like and typically are provided with a watertight, openable hatch cover, so that workmen may gain access to the interior of the vault when necessary. Because hatch covers of this type are exposed to very severe operating conditions, they must be ruggedly built and must close with a highly effective, watertight seal. The invention is directed to improvements in the design and construction of watertight hatch covers for the purposes described.
An improved form of watertight hatch cover according to the invention incorporates a rugged surrounding metal frame, which can be embedded in a sidewalk or the like and is provided with a recessed sealing gasket. An openable hatch cover is received within the frame, so as to lie flush with the frame and the surrounding grade level, when the hatch is closed. To secure the hatch tightly in a closed position, radially extendable locking bars are provided on the underside of the hatch, and these can be projected radially relative to the frame, into cooperating relation to closing cams provided on the frame. The cooperation between the locking bars and the closing cams serves to draw the hatch cover tightly down against and in sealing contact with the sealing gasket. Typically, externally accessible means are provided for securing the locking bars in their extended positions, so that the vault is accessible only to authorized persons possessing an appropriate opening key.
In an advantageous embodiment of the invention, a hatch cover is hinged at one side to its frame and arranged to be opened and closed by pivoting motion. A rotatable actuating element is provided in the center of the hatch cover, accessible from above by authorized personnel. The actuator is connected to a plurality of radially extending locking bars, slidably mounted on the underneath side of the hatch cover. Rotation of the actuating element in one direction or the other causes radial retraction or extension of the locking bars. In a typical hatch cover arrangement according to the invention, the hatch is of rectangular configuration and the locking bars extend to the corner areas thereof. Cam follower elements, preferably wheels, are provided at the ends of the locking bars. As the bars are extended toward the corners of the hatch, the cam follower elements engage wedge-like closing cams, progressively displacing the hatch cover in a downward direction during the final extension movements of the locking bars. The hatch cover is thus forcibly displaced downward at its four corner areas to effect a tight, uniform, watertight seal between the hatch cover and a sealing gasket provided in the surrounding frame.
In a structure in which the hatch cover is recessed within a surrounding frame, as contemplated herein, water and debris can find its way into the narrow gap between the edges of the hatch cover and the surrounding frame. In winter time, any water present can turn to ice. Thus, the hatch cover commonly can become rather tightly jammed within its surrounding frame and correspondingly difficult to open. As a feature of the invention, at least those locking bars located on the side opposite the hinge are arranged for cooperation with opening cams, provided at the corners of the surrounding frame. When the locking bars are retracted for opening of the hatch cover, the cam followers, in the last stages of opening motion of the locking bars, engage wedge-like opening cams which forcibly displace the locking bars and the hatch cover upwardly. The upward displacement of the hatch cover extends over only a short distance, but is accomplished with a high mechanical advantage. This causes the hatch cover to be broken free of its restricting environment, be it ice or debris. Once the hatch cover has been initially broken free, it can easily be opened in the conventional manner.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention and to the accompanying drawings.